This invention relates to a method and apparatus for cutting parts from thin sheet metal in a laser cutting machine, and the thin sheet metal may be in coiled form.
German Patent DE 28 35 476 B1 describes a device for feeding a sheet metal strip from a coil into a metal processing machine such as a punch or stamping press, with a coil-carrying reel followed by feed and straightening rollers for the metal strip being uncoiled. The metal strip is uncoiled in a stepwise fashion, and its advance is controlled by means of a pressure spindle bearing on the strip and by a reel brake pressing against the coil direction. In a similar context, German Patent Publication DE 40 20 839 describes the cutting of the uncoiled metal strip into stackable blanks that are fed into a pressing tool. In that case, the sheet metal strip is placed in a pressing die, and particularly careful handling of the blank's surface does not appear to be necessary.
For cutting sheet metal blanks from coiled material by means of a laser, U.S. Pat. No. 6,563,081 describes the continuous unrolling of the coil, straightening the metal strip and feeding the straightened strip underneath and through a bridge upon which a focusing head is mounted for motion crosswise relative to the direction of travel of the metal strip. To permit a reverse movement of the strip for the cutting of complex patterns, an intermediate compartment allows the strip to sag in a loop when it is retracted from the processing platform. However, the intermediate compartment limits the reverse movement capability of the strip. This constant reciprocal movement of the metal strip on the processing platform makes surface scratching of the strip inevitable. There is also a risk that, as partly cut blanks move backward, they can dip into the longitudinal channel and are either bent out of shape or cause a jam.
Without identifying the source, U.S. Pat. No. 6,563,081 refers to a “known” prior art technique wherein the metal strip is uncoiled in stepwise fashion or the individual blanks are placed on a processing platform. In a fixed head unit, teeth grip the strip along its edges and guide it under the head by means of articulated arms. Alternatively, the focusing head is moved in two axial directions as the metal strip is advanced in stepwise fashion and placed on the processing platform. The drawback here is that larger blanks which protrude beyond the processing platform cannot be cut, some cut blanks are lost, and removing the toxic smoke requires a complex system.
It is the object of this invention to provide a novel method and apparatus for cutting sheet metal blanks from a coiled thin metal strip which is advanced in stepwise fashion, without any blanks being jammed, scratched or lost.
It is also an object to provide such a method and apparatus which can be used to process separate flat plates.
Another object is to provide a method and apparatus which is easy to operate and adjust for producing different blanks.